The term “acoustic microscopy” traditionally referred to the use of high frequency ultrasound to probe the microstructural form and composition of an object. Traditional pulse/echo techniques were employed. Measurement of acoustic amplitude and phase were done either by contacting ultrasonic probes, or by optical interferometry through a microscope. Data for a particular point on a subject surface were obtained and useful images of the overall surface could be built up by raster scanning the object beneath the microscope.
The prevalence of micrometer scale mechanical features, microelectromechanical structures (MEMS), integrated circuits, microstructured materials, etc. is increasing. An accompanying need exists to probe the surface and subsurface physical, mechanical, and defect characteristics of such features, devices, and materials. However, conventional acoustic microscopy does not possess adequate resolution to produce reliable images and does not produce a real-time image of a surface since data is compiled over time from individual analysis points. Accordingly, the usefulness of conventional techniques are limited.
Telschow, et al., “UHF Acoustic Microscopic Imaging of Resonator Motion,” 2000 IEEE Ultrasonics Symposium Proceedings, October 22-25, Vol. 1, 631-634 (2000), describe a beginning attempt at overcoming the deficiencies of acoustic microscopy indicated above and otherwise recognized by those of ordinary skill. Telschow, et al. acknowledge the desirability of obtaining images of ultrasonic motion over an entire surface of a subject within a single video frame. The reference also indicates success at megaHertz (MHz) frequencies, although not using microscopic techniques. As acoustic wavelengths get smaller (due to increasing frequency), they become capable of detecting smaller features and defects. MHz frequencies are but a beginning step in developing significantly useful imaging technology.
There exists a heretofore unrealized need to provide methods and apparatuses for accomplishing full-field, real-time imaging developed on the foundational principles of acoustic microscopy. While the advances to-date have provided improvements, they have not yet enabled one of ordinary skill to take the next leap into microscopic imaging with frequencies high enough to probe at useful resolutions.